Size Reduction

IFPRI Strategic Plan for Supporting Research in Size Reduction of Particulate Solids

Since the formation of IFPRI in 1979, its membership has been interested in the millennia-old process of size reduction, as it is the most energy intensive and inefficient particulate solids process and is also complex and the least understood. From the process engineering view point, the interest is in the energy utilisation and scale-up of various mill types, issues which have been besetting the industry forever. The materials-related aspects of interest are:

the smallest possible particle size, which could be comminuted, for a number of applications, such as the highly sought-after ‘top-down’ approach to nano-particle production;

the most desirable, yet challenging issue of having predictive size distribution of comminuted materials for feed materials larger than the above limit;

appropriate methods of application of stresses for a given material, i.e. point loading, distributed loading or loading accompanied by frictional traction, low or high strain rate loading, level of stresses required for comminution to a certain size range, and environmental conditions;

For crystalline solids, the role of crystal habit in affecting the product properties, in particular the changes brought about by milling in surface structure, properties and chemical activity, phase transformations, and functionality.

For amorphous solids, the chemical and physical stability following size reduction.

In a liquid environment can the surfaces be modified and in a gas environment, what is the effect of humidity?

IFPRI’s approach in defining the strategic research direction and new programmes is by consultation with the members, helped by workshops in which the states of the art and understanding are critically reviewed and analysed by leading experts in the field. IFPRI organised a strategic workshop in 2011 to identify research needs to achieve a better understanding of size reduction. Nine topics were addressed: energy utilisation, scale-up, current capabilities in modelling, role of feed properties, solid state and structure, product characteristics/attributes, milling aids, mechano-chemical activation, nano-milling and undesirable effects, such as electrostatics, contamination and wear. Considering the generic needs of IFPRI members, the workshop identified five paramount research priority topics:

Review of dry/wet grinding and processing aids

Molecular modelling of mechanical properties

Manufacturing micron sized advanced materials: the mill as a reactor

‘Grindability’ test: modelling, measurement and mill fingerprinting

Assessment of energy utilisation distribution throughout the mill across scales